This research is concerned primarily with certain endogenous potentials of the brain which can be recorded from the human scalp. The major objective is to clarify essential questions concerning the functional significance of specific endogenous potentials associated with discrimination and decision making. These investigations constitute one step toward comprehending how the brain is the substratum for human cognition. Additional aims are to delineate the scalp distribution of event-related potentials related to semantic versus purely sensory discriminations, and to apply relevant findings to issues pertaining to the manner in which information is stored in long-term memory.